1. Field of the Invention
The present invention relates to a pilfer-proof synthetic resin cap.
2. Description of the Prior Art
A pilfer-proof synthetic resin cap has heretofore been known to have a top panel, a cylindrical skirt portion hung from the peripheral edge of the top panel, a circumferential band provided at the lower end of the cylindrical skirt portion via a weakened line, and flap pieces provided maintaining a predetermined distance on the inner surface of the circumferential band portion to engage with a jaw portion formed at the mouth of a container, and has been widely put into practical use.
With this cap, the circumferential band portion is secured by the flap pieces to the mouth of the container. When the cap is opened, therefore, the weakened line is broken and the circumferential band portion only remains at the mouth of the container to exhibit a pilfer-proof function.
In the above cap, however, the flap pieces are not strong enough to fully engage the jaw portion formed at the mouth of the container and, besides, the weakened line is frequently not broken even when the cap is open; i.e., the cap is often entirely removed together with the circumferential band.
Furthermore, some gap is formed between the lower end of the circumferential band and the mouth of the container, and mischief is often done using this gap.
Japanese Laid-Open Patent Publication No. 296666/1990 discloses a cap having an upwardly directed flexible tab formed on the circumferential band portion and interference beads formed at the lower end of the circumferential band to inwardly protrude.
In the cap of the above prior art, an increased engaging force is obtained between the circumferential band and the jaw portion formed at the mouth of the container due to the flexible tab and the interference beads that work in cooperation together. Therefore, the cap that is opened is effectively prevented from being entirely removed, and the gap formed between the lower end of the circumferential band and the mouth of the container is filled with the interference beads. According to the above prior art, however, the cap is molded very difficulty since it has two kinds of protrusions, i.e., flexible tab and interference beads on the inside of the circumferential band. That is, the caps of this type are usually produced by such molding means as injection molding using a suitable metal mold. In the case of the above cap, however, is very difficult to remove the, metal mold after the molding operation because of the shape of the circumferential band portion. In fact, the above prior art does not at all describe concerning the molding means.